Sitting on an Italian hilltop is this surreal fortress built by the mad inventor of electrohomeopathy.

Venice's "Island of the Mad."

A large grotto built in the 16th century amidst Florence's famous Boboli gardens.

Thousands of well-dressed mummies below a monastery.

According to the local folklore, the myriad colors of this lake are the result of a lovelorn wizard's blunder.

The doodles of a genius line the walls of a secret room under the Medici Chapel, where they were hidden for nearly 500 years.

Stalactites and stalagmites in a beautifully lit cave.

This hidden Art Nouveau courtyard is an opulent feast for the eyes.

This community on a small Venetian island has taken to painting their houses in bright neon hues.

A submerged archeological park still holds the wonders of a Roman Sodom.

An Italian crevasse filled with abandoned buildings gives visitors a look at the world without humans.

A 16th-century horror show built in a lovely Italian garden.

Hundreds of lucky felines haunt the ruins where Caesar was murdered.

This hermitage celebrates the legend of Emperor Constantine's healing from leprosy.

Remnants of a 4th-century church with vivid medieval frescoes and ancient sarcophagi hide beneath this old basilica.

This ancient market is often referred to as the oldest shopping mall in the world.

Also known as the Square Colosseum, this building is a prime example of fascist-era rationalist architecture.

This park on the outskirts of Rome boasts two ancient Roman aqueducts and a medieval tower.

The ruins of an abbey believed to have been founded by Charlemagne in the 9th century.

A magnificent waterfall is also home to the remains of a Roman hydraulic engineering system.

The first Russian Orthodox church in the Catholic city of Rome in almost a thousand years.

The best preserved Paleochristian basilica in Rome hides a number of oddities and secrets.

Brass cobblestones mark the places where individual Holocaust victims were taken from their homes.

A treasure trove of Renaissance-era funerary art in a Roman church built on top of Nero's grave.